When constructing a command response, mongos may need to refresh its set of signing keys if the key for the cluster time isn’t currently known. If the client disconnects before this refresh, the resulting error is not properly handled and causes mongos to crash.
mongos will crash with a message saying “operation was interrupted because a client disconnected. terminate() called.”
This affects 4.2.6 and earlier versions of 4.2.
The fix will be included in 4.4.0 and 4.2.7.